Anthony Weiner is to run for mayor of New York City. Photograph: Anthony Behar/Sipa USA / Rex Fea

Former congressman Anthony Weiner, whose career imploded after he sent a string of sexually suggestive tweets two years ago plans to run for New York City mayor.

"I made some big mistakes and I know I let a lot of people down, but I also learned some tough lessons," Weiner said in the video. "I'm running for mayor because I've been fighting for the middle class and those struggling to make it my entire life. And I hope I get a second chance."

Weiner is embarking on an audacious comeback, given that his tweeted crotch-shot became emblazoned on the nation's consciousness. He had said last month he was considering entering the race.

The Democrat is jumping into a crowded field for September's primary. He is arriving with some significant advantages, including $4.8m in campaign funds, the possibility of a further $1m in matching public funds, and polls showing him ahead of all but one other Democrat. there is also no end of name recognition.

Weiner's participation makes a runoff more likely. Many political observers feel he could at least get to the second round.

But Weiner also has continued to contend with questions about his character and the scandal that sank his career.

After a photo of a man's bulging, underwear-clad groin appeared on his Twitter account in 2011, he initially claimed his account had been hacked. After more photos emerged – including one of him bare-chested in his congressional office – the married congressman eventually owned up to exchanging racy messages with several women, saying he'd never met any of them. He soon resigned from his House seat.

In recent interviews, Weiner has said he shouldn't have lied but did it because he wanted to keep the truth from his then-pregnant wife, Huma Abedin, a longtime aide to former secretary of state, Hillary Rodham Clinton. She told the New York Times Magazine she has forgiven him.

Weiner has taken a series of steps recently to rehabilitate his image and reintroduce himself, including the lengthy magazine profile and a series of local TV interviews. He also has released a platform of sorts, a list of ideas styled as a blueprint for helping the city's middle class thrive. He's made a point of highlighting one or more of the concepts on most days, via his newly revived Twitter presence.

Weiner was known during his seven terms in the House as a vigorous defender of Democratic viewpoints, unafraid to get combative whether it was on cable TV or the House floor, and as a tireless and instinctive politician.

"Anybody who underestimates Anthony Weiner's ambition is a fool. And anybody who underestimates his ability as a candidate is a fool," retired Hunter College political science professor Kenneth Sherrill said.

In a recent NBC New York-Marist Poll, half of respondents said they wouldn't even consider him, though the survey also showed that more registered Democrats now have a favourable than unfavourable impression of him.